Conventionally, various aerofoils have been proposed for the stationary vanes of gas turbines and steam turbines to optimize efficiency. For instance, Japanese patent laid open (kokai) publication No. 10-196303 discloses a proposal in which the aerofoil is curved along the span-wise direction either to the back or belly of the aerofoil so as to minimize the loss due to the generation of secondary flows. It is also known to slightly twist the aerofoil around a span axis to thereby vary the blade inlet angle of the aerofoil along the span-wise direction. Such aerofoils are called as three-dimensional aerofoils, and are effective in improving the efficiency of the turbine. However, as they have to be made either by casting or by computer-controlled machining, the manufacturing process is both complex and expensive.